FTIR measurements—standards and accuracy

Abstract Many applications of mid-infrared (MIR) spectrophotometry now require known levels of uncertainty in both the abscissa and ordinate axes. The National Physical Laboratory (NPL) has long provided MIR transfer standards of regular transmittance, regular reflectance, hemispherical reflectance, and also of wavenumber, which can be used to test and validate industrial infrared spectrometers and their measurements. A recent addition to this range of calibration artefacts is a multi-angle reflectance standard. Measurements carried out to establish and disseminate optical radiation scales need to be made to well-understood and quantified uncertainties. NPL is carrying out research, as are other measurement institutes such as the National Institute of Standards and Technology (NIST), to enable the application of Fourier transform (FT) instrumentation to these types of measurements. This work is necessary because of the many categories of ordinate error in FT spectrometry [Spectrosc. Eur. 7 (1995) 16; Anal. Chim. Acta 380 (1999) 369] and the lack of validated methods for identifying, eliminating, or minimising and quantifying them.